1. Field of the Invention
This invention relates to image amplification and more specifically to a multi-core optical fiber image amplifier.
2. Description of the Related Art
Image amplification is typically not performed optically on the incident image. The common approach is to detect the light photons incident on a pixilated array, generate electrons, amplify the electron number, and then detect the number of electrons in each pixel of an electronics channel.
Electronic amplification is typically noisy and does not preserve either the phase or spectrum of the incident light field. Furthermore, if additional optical processing is to be performed the amplified electronic image must be converted back into an optical image. This O-E-O conversion limits the performance of the amplifier. Other approaches use, for example, a microchannel plate or wave mixing techniques.
A microchannel plate is a device which detects light at a photocathode and converts the incident photons to electrons. The plate creates an avalanche of electrons that are directed to hit a phosphor screen, which emits amplified light. A focal plane array is placed after the phosphor to detect the amplified light. The amplified light is at a different wavelength, all of the original phase information is lost and suffers from a lot of noise due to electron amplification.
Wave mixing uses the nonlinear mixing properties in photorefractive crystals to provide image amplification. The image to be amplified interferes with a strong pump beam—and the diffracted beam contains a copy of the image riding on top of a higher power beam. Examples of wave mixing amplifiers are described in S. Breugnot et al. “Low-noise preamplifier for multistage photorefractive image amplification” Optics Letters, Vol. 20, No. 14, p. 1568, Jul. 15, 1995; Sang-Kyung Choi et al. “Noiseless Optical Amplification of Images” Physical Review Letters, Volume 83, No. 10, p. 1938, Sep. 6, 1999 and E Lantzy et al. “Parametric amplification of images” Quantum Semiclass. Opt. 9 (1997) 279-286.
Coherent passive fiber bundles are used to transfer and/or magnify optical images, but not amplify. The fiber bundles may comprise individual passive fibers with a single core or a single fiber with multiple cores. SCHOTT's Wound Fiber Bundle includes a bundle of multi fibers with each multi fiber including an n×m array of passive core structures.